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RX J1856.5-3754
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KS 1731-260:
A Cool Neutron Star in the Constellation Ophiuchus


KS 1731-260
Credit: NASA/CXC/Wijnands et al.

Chandra' s observation in March of 2001 of the neutron star KS 1731-260 (pale blue dot just above the middle of the image) showed that it is a remarkably 'cool' 3 million degrees Celsius. This low temperature was surprising because in the period 1988 to 2000 the neutron star was shining brightly in X-rays due to the heavy bombardment of gas from a companion star, not visible here. A neutron star temperature of 10 million degrees or more was expected.

A possible explanation for the relatively low temperature of KS 1731-260 in its present quiet state is that it was in a deep freeze for a thousand years before 1988 and took 12 years of heating just to get to the temperature it is today. If so, it may represent a new type of neutron star system that stops accreting gas for a long period of time, and there could be hundreds of undetected, cold neutron stars in our Galaxy.

Fast Facts for KS 1731-260:
Credit  NASA/CXC/Wijnands et al.
Scale  Image is 1 arcmin across.
Category  Neutron Stars/X-ray Binaries
Coordinates (J2000)  RA 17h 34m 13.5s | Dec -26 05' 16.8
Constellation  Ophiuchus
Observation Dates  March 27 2001
Observation Time  6 hours
Obs. IDs  2428
Color Code  Intensity
Instrument  ACIS
Distance Estimate  23,000 light years
Release Date  September 06, 2001